Sheatheria
The Sheatheria Project is an exercise in plausible evolutionary progression in an implausible environment. Sheatheria is a large, superficially Earth-like rocky planet with a circumference a little over twice that of Earth's and just over over four a half times the surface area of Earth itself (approximately 894 million square miles - see graphic of Earth compared to Sheatheria here for an idea of how big we're talking). Despite its enormity, however, as a result of a less dense composition than our world, the planet still hosts a gravitational pull of just 1g, identical to modern-day Earth. The planet's atmosphere is functionally comparable to that of modern Earth, with a little more oxygen and just a hair less carbon dioxide. The planetary environment is differentiated from our own in several respects, however, including an elliptical orbit which is significantly ovular as to produce seasonal change as it moves further and closer to its sun throughout the span of the year, and a reversed climate arrangement with tropical polar regions and a seasonal ice-locked equator. Sheatheria as it falls is equivalent to Mars in its distance from the sun and as such would fall outside the readily habitable planetary zone were it not for a very special circumstance. The fundamental nature of the planet of Sheatheria straddles the line between fantasy and physical possibility - intentionally so. The theme of the project is not the explanation of how such a world could come to exist. Rather, the theme is what could life do on such a strange planet if it could?. The life that inhabits the strange world of Sheatheria is not its own. Rather, it has been taken through most mysterious means from the varied allotment of charismatic Earthly organisms known to exist or have existed from throughout all of Earth's major life-bearing epochs, with each new wave being introduced in its specific era. As such, the world exists as one of the grandest examples of terraforming throughout all the cosmos, one which continues to this day. Waves of migrants to the world from our own are introduced seemingly at random rather than intentional transport, through apparent rifts in the very fabric of space and time that may last hours or centuries. The process seems to have begun just before the genesis of the very first multicellular life on Earth in the Ediacaran, 625 million years ago, and to have continued at least of 25 times since, at one point appearing approximately every 15 million years but growing less frequent towards the modern day. The most recent introduction is a very new one: it occurred just four thousand years ago, but brought with it but a tiny sampling of life. With each new flood of flora and fauna, a new cast of characters, comprising prominent members of major groups of each era (big and small) are thrown and scattered throughout the global ecosystem, each introduction building upon the last. Through it all, some life prospers for a time only to dwindle out when a new wave of immigrants, more adaptable than those who came before them, proves too big a blow to the environment and the ecosystem temporarily falls into a state of chaos. Just as often the reverse is true; new lifeforms must very quickly alter their habits or die out in short order, niches they've adapted in their home world already taken in their new one - and as time goes on, the environment becoming increasingly full and stable, the number of new survivors grows increasingly small. The end result is an ever-changing system of strange and convoluted evolutionary paths and mixed and matched ecological communities that would have never had the opportunity to form on planet Earth. These results can be brilliant, breathtaking, and beautiful. They can also be bizzare, frightening, and wildly disconcerting. You can never be sure what the future will bring to a planet in a constant state of flux, in a world simultaneously familiar and fantastical. History: Sheatheria is a planet based on so many strange disparities that it seems almost certain to be an artificially crafted world, but if so, who or what great entity could have possibly engineered it is entirely unknown. It is far lighter than one would ever suspect for a planet its size - which even if not impossible is certainly improbable to occur by natural means - resulting in a most unexpectedly low gravity relative to its mass, and just what strange rules govern the presence of the planet's northern and southern force fields, on which the survival of all the planet's life depends, are equally mysterious. They too appear to have been present upon the planet since its initial genesis, for had they at any point in at least the last 600 million years been absent the planet would have quickly chilled to levels insufficient to support advanced life over most of its surface. They do seem to shift considerably towards and away from one another throughout the ages between this polar-centric state and a more over-lapping one where heat is distributed more evenly across the entire planet, where distinctions between the north or south bubbles are blurred and function as a single elongated energy globule. These 'bubbles' additionally have a tendency to reflect light beamed at the equator up again from the ground and towards both poles, which experience . As Sheatheria is not tilted on its axis, there is no seasonal change in the amount of sunlight the poles receive. However, even though the sun is always low on the horizon in the extreme polar regions these parts of the planet can still rival at midday the brightest of sunny days on Earth as a result of reflected equatorial light. This lighting, reflected from beyond the horizon where the sun shines from directly overhead, radiates northward and southward from the equator and fills the polar skies with an even glow, turning a blue sky golden and evenly lit throughout. Further complicating the situation, though the majority of the polar region experiences a 16 hour day, a small circular area with radius of approximately 250 hundred miles upon the extreme north and south poles of the planet, which are always touched from one direction or another by the day-lit side of the planet, glow in eternal daylight for the full Sheatherian day length - a full 32 hours per day and every day of the year, knowing no night. The planet's environments are also heavily affected by the orbit of its two large moons - tides, in particular, can be very extreme, even leading to whole new ecosystems absent upon Earth. Sheatheria's temperate belt, which runs along the equator, is seasonal despite the fact that the polar energy shields do not change their influence significantly throughout the cycle of a single year. Instead, changes come from the planet's very wide and arcing 402 day long orbit around its sun. When the planet is nearer to the sun, the equator receives more warmth, and summer begins. As it moves further away in the autumn, temperatures gradually fall again and winter comes to the land. Throughout the year, it is only temperature, never sunlight, that brings winter to the landscape, and especially cold-hardy plants can continue to photosynthesize, even to grow, right through the cold season provided they are not buried beneath snow. Polar regions, insulated by their energy fields, remain warm the year round with growing seasons unaffected by temperature changes and dictated only by the availability of water. Sheatheria exhibits active plate tectonics and relatively predictable continental drift. When the first life reached it in the Ediacaran, it existed as a single super-continent with only isolated surrounding islands, which gave its very first colonists a clear path to spread far and wide over the land, carpeting bare rock in a healthy coating of microbes and rapidly filling up the atmosphere with oxygen. By the Permian, however, it had split into three distinct landmasses, east and west, which would provide two distinct environments for the formation of what what become two of Sheatheria's most distinct megafaunal lineages. In the west evolved the Megagnaths, a terrestrial clade which sprang up from the jawless fishes of the young ocean, while a world away arose the enigmatic Endosseans, a clade of early crustaceans which claimed the Eastern land and, without competition, radiated into a strange and magnificent array of megafauna supported by ossified internal tissues in addition to a remnant exoskeleton. The Triassic brought the gradual destruction of the two great continents. The East broke into two distinct land masses; one remained toward the north and collided with a north-bound Western continent, while the other half split southwards near to the bottom of the planet. This region would eventually become the south-polar landmass known as Aenvarna, and as it was flooded with new waves of colonists - Archosaurs and Synapsids, the majority of its native Endosseans would die out. However, a substantial portion its southernmost edge would soon break away into the far western sea. This landmass, Wumbus, would survive to the present without again touching another continent nor taking part in a single wave of Terran migration, caught in the gear-like circular grip of other tectonic plates, providing a strange and isolated haven for these and other representatives of Sheatheria's most primitive colonists. Its life would be forged from those hardy enough to reach it by air or sea, or those marooned there from the start. The Jurassic and up through the Cretaceous eras of Sheatheria brought more changes, as the East and West continents gradually became centered southwards and northwards, respectively. The north was larger and readily broke apart and reformed, providing numerous isolated environments for the survival and evolution of groups as diverse as the Megagnaths and Tyrannosaurs while the south remained relatively stable and isolated, providing a haven for such creatures as Therapsids from the Triassic and new migrants; primitive frogs which would give rise to an entirely new lineage of endothermic megafauna, the Ranamonarchians. This stability lasted until the last quarter of the Cretaceous, when a combination of the planet's shielding energy fields reaching the peak of their polar-centric cycle and the arrangement of continents cut oceanic currents and brought the planet into its first ice age. While polar regions stayed tropic, for the very first time temperatures at the extreme equator were left so cold as to produce a band of solid ice which lasted for more than 16 million years and completely divided the planet's hemispheres. Sea levels dropped markedly as a significant amount of water was locked up in ice at the equator, and continents gained considerable new area along their coastlines - briefly. For a short time, seas were low enough that a bridge of solid land appeared between the north and south, providing a gateway for a very abundant clade of Ornithopod dinosaurs to head northwards. As the ice receded right around the time the massive K-pg extinction shocked Earth, life on Sheatheria was just getting back to normal. The ice receded by the late Eocene, separating the hemispheres once more as primitive mammals and gallo-anser birds colonized the planet. Over the following millennia more modern mammals would follow, including ungulates, but Sheatheria wouldn't truly experience its next major evolutionary innovation until the introduction of the rodents just short of 50 million years ago. Two clades, the bipedal Theropodents and the strange, primitive Anomolospectrodonts would diversify from an epicenter on the new continent of Servallia towards Aenvarna to the south, Andromere to the north. Servallia now existed as an intermediate portion broken from Andromere that lie in between the top and bottom of the world as a scattered and almost disconnected series of isles. From here, both rodent clades would both radiate both north and southwards before Servallia was severed from Aenvarna once more by rising sea levels. Modern Sheatheria has again been gripped by an ice age. The equator is again frozen, the continents and energy fields having again tripped over one another in just the right way to result in a global drop in temperature, and the north and south are again isolated. The continents continue to be represented mainly by a single winding landmass in the north now known as Andromere, and the smaller, compact south polar land known as Aenvarna. In between them, the Servallian continent has broken apart to form the modern subcontinent, a withering series of islands and peninsulas, and the isolated landmasses of Gymnurus and Levester to the East, along with Atroxus to the north, which has collided to become one with Andromere and closed in the Lyran and Auroran inland seas from the rest of the ocean. What is still known as Servallia today is a shadow of its former self, lying attached at the southernmost edge of Andromere, trapped in the south below the belt of ice and nearly connected again to Aenvarna with its northern portion now completely attached to Andromere north of the ice belt and now known as Boreasia. Wumbus remains isolated to the far western sea, a fraction of its historical size by the result of erosion - but temporarily enlarged by sea levels that have dropped again in coincidence with the permanent new ice cap, which has already lasted longer than in the former age. Formed nineteen million years ago, after but a short reprieve in which Sheatheria's formerly globally tropical climate did not fully return, this ice age is believed to still be increasing in influence and possibly to last as long as forty million years. A modern trend seems to be emerging for a more temperate Sheatheria, and it may well be that ice ages such as this become the norm in future epochs. The Modern Biosphere: Life on Sheatheria today is a varied tapestry forged through the ages. The ultimate list of survivors, it consists of only the hardiest and most adaptable creatures of all time. Sheatheria's ecosystem is founded on green plants, and today most of these are grasses and other flowering plants, which can be considered even more diverse here than upon Earth, for they have readily colonized the sea. Both lichens and algae are more commonplace as large terrestrial organisms. Sheatheria's microcosm is inhabited by a varied assortment of arthropods from insects and arachnids to trilobites, as well as a high diversity of aquatic crustaceans, echinoderms and molluscs (gastropods and bivalves in particular). Megafauna today on Sheatheria is varied, but can be divided into a few broadly predominant groups. Ungulates are relatively diverse, and as a modern group are less divergent than many other lineages, while rodents, monotremes, and dasyuromorph marsupials fill in the majority of mammalian diversity. A smaller still number of surviving non-mammalian therapsids exist, most notably represented by Sunsharks, a volant form originally descended from oceanic ancestors. Ray-finned and cartilaginous fishes share the planet's waterways equally with the surviving ancestors of more basal jawless variations (which have also produced advanced terrestrial lineages), cephalopods, large gastropods and crustaceans, as well as many oceanic tetrapods and other groups depicted below. Reptiles are widely diverse, most particularly phytosaurs and squamates. Archosaurs are very well-represented, particularly by crocodiles and a wide variety of birds and other feathered coelurosaur dinosaurs, as well as a particularly diverse endemic ornithopod clade. Sheatheria also hosts a small number of extant pterosaurs and derived lineages of earlier oddball Archosaurimorphs. Sheatheria's most dominant true bird clades today are waterfowl and parrots. Sheatheria has no large carnivoran mammals, but mustelids are present. A representative list of Sheatheria's most notable endemic animal clades appears below. Category:Sheatheria